This invention relates to thermoplastic liners for pipes. Such liners may be applied during the initial manufacturing stage, or in later refurbishment and/or repair stages. In either case, the useful life of the pipe is significantly increased by the corrosion protection afforded by the use of such liners.
Pipe lining process are, of course, known in the art. U.S. Pat. Nos. 4,496,449; 4,394,202; 4,207,130; and 3,429,954; Canadian Pat. No. 1,084,224; and U.K. Pat. No. 2,084,686 are exemplary. These processes have not proven to be completely satisfactory, however. This invention relates to an improvement in a pipe lining concept disclosed in French Pat. No. 2,503,622 of Apr. 13, 1981. In that patent, a method of protecting pipe interiors with thermoplastic liners is disclosed, utilizing known shape memory characteristics of thermoplastic materials. Specifically, the patentee discloses the manufacture, by extrusion for example, of a cylindrical, thermoplastic pipe liner which has an elastic memory actuatable above a certain temperature, and wherein the outside diameter of the liner is approximately equal to the inside diameter of the pipe to be lined. The pipe liner is then deformed at a temperature at least equal to the memory activation temperature so as to alter and reduce the cross-sectional dimension oF the liner to facilitate insertion within the pipe to be lined. The temporarily deformed liner is preferably given a generally U-shaped cross-section, although other cross-sectional configurations such as H-shaped, or X-shaped are also contemplated. The liner is thereafter cooled to fix the liner in the temporarily deformed shape. After the deformed liner is inserted into the pipe, it is reheated to a temperature at least equal to the memory activation temperature to call the liner back to its original cylindrical shape.
In our own co-pending application Ser. No. 077,883, filed Jul. 27, 1987, now U.S. Pat. No. 4,863,365, and incorporated herein by reference, we have disclosed a specific method and apparatus for manufacturing temporarily deformed thermoplastic conduit which is particularly useful in carrying out the concept disclosed in French Pat. No. 8107346.
Generally, our earlier filed application discloses conventional extrusion of a thermoplastic material to a cylindrical shape at extrusion temperature. The cylindrical liner is subsequently cooled and passed between a series of shaping rollers to reform the cylindrical liner into a substantially U shaped configuration which reduces its cross-sectional dimensions by about 25%, after which the liner is cooled to ambient, and wound on a reel or spool.
The present invention relates to an improved method and apparatus for installing temporarily deformed pipe liner within a pipeline, expanding the deformed liner to its original cylindrical shape, taking additional steps causing the liner to conform even more precisely to the interior contour of the pipe, and flaring opposite ends of the liner into engagement with respective radially directed pipe flanges.
To this end, thermoplastic material is extruded and calibrated to obtain a cylindrical insert liner with a diameter slightly larger than the interior diameter of the pipe to be lined. Once extruded, the liner is temporarily collapsed in a manner described in our co-pending application Ser. No. 077,883, now U.S. Pat. No. 4,863,365, issued Sept. 5, 1989 and wound in continuous form on a spool or reel for transport to the site.
Before inserting the U-shaped liner in a pipe or pipeline section, a number of preparatory steps must be taken. For example, after accessing the pipe to be lined by existing man or access holes, or by digging new access holes, the pipe connections must be broken and the interior of the pipe or pipeline section must be cleaned to remove all loose debris and/or sediment therein. Subsequently, a pulling or pilot line must be threaded through the pipeline to enable the U-shaped liner to be pulled into the pipe from the downstream end. In this regard, throughout this specification, "upstream" refers to that end of the pipe into which the liner is inserted, and "downstream" refers to the end remote from the insertion end. In addition, the term "pipe" is used hereinafter to refer to single, individual lengths of pipe, as well as to a plurality of individual lengths joined together to form a pipeline or section of pipeline. In other words, "pipe" refers to any one or more lengths of pipe to be lined in accordance with this invention. Moreover, regardless of the number of individual lengths of pipe to be lined, typically, the open ends of the pipe or pipes, which define the overall length to be lined, are provided with conventional radial flanges to facilitate attachment to adjacent pipe sections. Such flanges are also utilized in conjunction with the installation process and apparatus of this invention as explained in greater detail below.
The cleaning and threading operations may be effected by a single brush pig of conventional design. At the same time, the brush pig is utilized to pass the pilot or pulling line through the pipe. To facilitate not only the pigging operation, but the liner insertion and expansion operations as well, a tubular manifold, which opens into the pipe at one end and which is closed by a removable flange at the other end, is applied to each end of the pipe, via the above-described radial flanges and fasteners such as bolts or the like. Prior to attaching the manifold at the upstream end, the brush pig is introduced into the manifold, and a pulling or pilot line is fed into a vent in the manifold and attached to the trailing end of the pig.
Once the manifolds are attached at either end of the pipe, liquid or air is supplied behind the pig to drive it the length of the pipe. At the same time, a relief valve in the downstream manifold permits air ahead of the pig to be released from the pipe interior. Brushes attached to the front of the pig clean the interior pipe wall surface in a manner well understood by those skilled in the art.
When the pig and pulling lines have reached the downstream end of the pipe, the downstream manifold is opened and the pig removed. The pulling line is then attached to a downstream winch or other suitable winding device.
At the upstream end, the upstream manifold is opened and the pilot or pulling line cut from the supply reel. The line is then drawn through the open manifold and attached to a lead end of the U-shaped liner. The U-shaped liner may then be pulled from its own supply reel into the pipe via actuation of the downstream winch or other suitable winding device.
It will be appreciated that depending on the length of pipe, the pressure available to push the pig through the pipe, and the tensile strength of the pulling line, a multiple stage process may be required to thread the final pulling line through the pipe. For example, for long sections of pipe on the order of 2 miles or even longer, or where there is a leak in the pipe, the pressure build-up in the pipe may not be sufficient to push the pig and, at the same time, pull a line or cable of the required strength through the pipe. In this case, a relatively light, so-called "fishing line" is initially threaded through the pipe by a relatively lightweight pig, followed by one or more increasingly stronger lines, drawn by larger pigs, until the final pulling line or cable is drawn through the pipe.
Once the liner is drawn into the pipe via the downstream winch, it is cut to an appropriate length, such that a relatively short section of liner extends beyond either end of the pipe, i.e., to approximately the length of the pipe section itself plus upstream and downstream manifolds at either end. Subsequently, packer/expander assemblies are introduced into the manifolds to seal the liner ends and to mechanically initiate expansion of the liner. Thereafter, fluid, preferably hot liquid from a closed boiler system, is supplied through one of the packer/expander assemblies and into the pipe to reheat the liner. During the reheating stage, an outlet valve in the manifold opposite that through which the hot liquid is supplied, is left partially open to allow the hot liquid to flow through, until the desired temperature is achieved. Once the liner has reached the desired temperature, it will begin to assume its original cylindrical shape. At the same time pressure within the liner rises. preferably to about 7 bars in a first pressurizing stage.
It is often the case, however, that the pipe itself may not be perfectly round along its entire length and, therefore, absent some further step, there may be annular or other pockets of air between the liner and the inner pipe wall.
According to this invention, the outlet valve is adjusted so that the pressure within the liner is increased in a second stage to about 15 bars to cause the liner to conform more precisely to the inner surface contours of the pipe.
Subsequently, the packer/expander assemblies are removed and the hot liquid, such as water, is emptied from the pipe. An expansion pig is then introduced into the upstream manifold to traverse the pipeline while the latter is still hot, and to apply a radially outwardly directed force about the circumference of the liner to squeeze out any remaining air between the liner and pipe to thereby ensure even further conformance to the inner pipe wall, including weldments and other surface irregularities. This second pig is driven through the pipeline with cold water which tends to "freeze" the liner in place.
Once liner expansion within the pipe is completed, the upstream and downstream manifolds are removed, and the liner ends are reheated and flared into contact with the blind flanges of the pipe, as described in further detail below.
By this invention, pipes of between 2 and 24 inches in diameter, and as long as two miles or more may be fitted with a continuous liner to provide ideal corrosion protection in both new and existing corroded pipes.
Other advantages of this invention include:
1. Structural characteristics of the pipe to be relined are preserved while the thickness of the U-Liner wall can be from 3.5 to 18 mm, depending on design requirements. The minimal reduced inside diameter will be compensated by the exceptional flow coefficient of the thermoplastic liner.
2. In the case of new pipe projects, U-Liner can be used to avoid the need for expensive materials such as stainless steel or alloys for transport of highly corrosive products. In most cases, the flow inside the plastic liner will be more efficient than if stainless steel or alloy pipes are used.
3. Lining of internally corrodible pipes will provide operators with longer life in both new and repaired pipelines, without costly total replacement of pipe sections due to corrosion damage. This will effectively reduce repair and maintenance downtime and therefore greatly reduce production loss.
4. Since the U-Liner can be inserted in very long sections, this method simplifies the often difficult and much protested surface disturbance of right-of-way in environmentally sensitive areas or across urban concentrations of people and traffic.
5. Although the normal use life expectancy of the thermoplastic lining is up to twenty years, unexpected damage can be repaired economically due to the easy removal and replacement of the U-Liner and its relatively minimal cost. The thermoplastic insert U-Liner will restore corroded pipes to original flow quality and eliminate further abrasion and corrosion damage to the steel pipe walls, thus substantially lengthening the economic life of the installation.
6. The process is simple, fast and cost effective, with minimum downtime.
In a preferred embodiment, the pipe liner is constructed of high density polyethylene (HDPE), but other thermoplastic materials may also be employed.
The preferred HDPE liner material has been tested with over 280 chemicals that might be expected to floW through a pipeline and the following observations have been reported relating to the above identified HDPE which are particularly relevant to this invention:
(a) high resistance to H.sub.2 S, CO.sub.2 and NaCl; PA1 (b) excellent for transporting gases; PA1 (c) cross-linkable to handle products at high temperatures (250.degree. F.); PA1 (d) stability in aging; PA1 (e) low roughness coefficient of 0.020; PA1 (f) does not retain deposits or sediments.
The invention as described herein has applications to many types of pipeline, including water and mud injection; oil and gas; vapors and fumes; saltwater; utility sewage and drainage; gas gathering and distribution, etc.
Other objects and advantages will become apparent from the detailed description of the invention which follows.